Embodiments of the present invention relate to mask settings for a signal analyzer, especially to a signal analyzer featuring automatic mask settings and methods for realizing these functions.
A system such as a wireless communication system for a mobile phone requires tests for confirming whether the used signals have no error. A signal analyzer may be used for measuring such a signal under test (SUT). The signal analyzer converts the SUT to digital data of time domain and then produces spectrum data that is digital data of frequency domain. The spectrum data may be obtain using a fast Fourier transform (FFT) or similar calculation. The obtained data is displayed as waveforms or numerical values on a display screen of the signal analyzer. The signal analyzer can provide not only the spectrum data of the SUT but also the time domain data corresponding to the spectrum data so that it can provide various signal analysis through digital calculation from two viewpoints of frequency domain and time domain. U.S. Pat. No. 6,377,617 discloses a technology that produces frequency and time domain data while correlating them each other, for example.
FIG. 1 (Prior Art) is a block diagram of a signal analyzer 10. The signal analyzer 10 has, in addition to the blocks shown in FIG. 1, functions and hardware equivalent to a PC though they are not shown. It adopts a general-purpose CPU typical of a PC, provides various settings through graphical user interface with keyboard and mouse, and can store large amount of data and program in a hard disk drive (HDD).
An input attenuator 12 adjusts the SUT to a proper level and provides it to an analog down converter 20. The down converter 20 has mixer 14, local oscillator 16 and band pass filter 18 and down converts frequencies of an input signal to produce an intermediate frequency (IF) signal with an analog process. An analog to digital converter (ADC) 22 converts the analog IF signal to digital data (time domain data). A memory 24 stores the digital data of the IF signal. A digital signal processor (DSP) 26 reads out the IF signal data from the memory 24 and conducts digital down conversion and fast Fourier transform (FFT) to produce spectrum data of frequency domain data. The spectrum data is stored in the memory 24 and then displayed as waveforms or numerical values by a display 30. The DSP 26 may be used for other various calculations according to program stored in the HDD. A trigger detection circuit 28 receives the time domain data from the ADC 22 and the spectrum data from the DSP 26 to identify data that satisfies a user set trigger condition and controls the memory 24 to keep the user desired time domain data and/or spectrum data in the memory 24.
The memory 24 may be a RAM that can provide faster data reading and writing than the HDD so that it is suitable for temporarily keeping the time domain data and/or the spectrum data that are produced fast. An HDD has a large capacity but the data reading/writing is slow so that it is difficult to continuously record the fast time domain data and/or spectrum data. Therefore, a trigger condition is provided, the data satisfying the trigger condition is temporarily stored in the memory 24 and then only necessary data is stored in the HDD.
Various trigger condition settings controlled with the trigger detection circuit 28 are known. The trigger condition settings using time domain data are similar to those of a digital oscilloscope. In a conventional trigger setting, a given threshold is set, time domain data of the SUT around a trigger point, or an SUT portion that is over the threshold, is being stored into a memory as far as the memory capacity accepts to display it as a waveform. In addition to the traditional trigger condition setting, another trigger condition setting is widely used that a mask is set to be compared with a displayed waveform to determine whether the waveform enters the mask. As for proper mask settings, U.S. Pat. No. 6,728,648 (corresponding to Japanese patent 3,670,944) discloses that it displays a waveform based on the conventional trigger condition, and then automatically adjusts test mask position as a normal waveform not to touch the mask.
A trigger condition setting using a mask for spectrum data is also known. For example, U.S. Patent Publication 2003/0085925 (corresponding to Japanese patent publication 2003-194855) discloses that spectrum data is displayed as a waveform and a mask for the waveform is set and edited.
Generally it is difficult to capture an intermittent phenomenon that occurs less frequently. But if a signal under test (SUT) is measured with a signal analyzer and if it is roughly predicted when and around which frequency the intermittent phenomenon occurs, the intermittent phenomena may be captured effectively as frequency domain data by setting frequency mask trigger based on the prediction before acquiring the SUT data. Conversely, if it can not be predicted the capture efficiency dramatically drops.
In case that it is difficult to predict how to set a mask or even a case that it can be predicted, if a user can set a trigger condition using a mask easily desired portions such as defect in the SUT can be easily captured in a memory of a signal analyzer.
Therefore, what is desired is to make a signal analyzer automatically set a mask to easily capture desired time domain data or frequency domain data in an SUT.